Power hammer for mechanical tamping



Nov. 9, 1954 2,693,733

W. D. FISH POWER HAMMER FOR MECHANICAL TAMPING Filed Feb. 9, 1950 H220rn@ United States Patent C) POWER HAMMER Fon MECHANICAL TAMPING WalterD..Fish, ClaremonQNL HL, assignor to Joy Manufacturing Company,Pittsburgh, Pa., a corporation of Pennsylvania Application February 9,1950, Serial No. 143,284

20v Claims. (Cl. 86-20) This invention relates: to` power hammers andmore particularly to apower hammer adapted for association withatampingv stick for mechanically tamping powder or dynamite into a holeto be charged.

In a known method of tamping a blasting charge in a blast hole to becharged, a tamping stick or rod is inserted in a blast hole formed inthe working face of the earth. or rock strata to be blasted, such as theface of. an underground mine or tunnel, anda power hammer isassociatedwith the tamping stick for imparting a series of rapid,relatively light, blows or vibratory jars to the outer end of the.tamping stick to elect mechanical tamping of the powder or dynamitecharge in the hole. The present invention contemplates the provision ofan improved power hammer designed for association with the tamping stickor rod whereby a series of vibratory jars may be imparted to the stickto eiect rapid tamping of the blasting charge and with a minimum ofeffort and danger. The power hammer ofthe present invention is designedaxially to receive and lit over the tamping stick and has a releasableconnection with the stick whereby the hammer may impart vibratoryy jarsto the stick at any desired point at which the hammer is located axiallyof the stick. The power hammer of the present invention embodiesareleasable resilient` gripping device or yieldable clamp whereby thehammer tool may grip thetamping stick and a hammer motor embodied in thetool may impart a series of rapid, relatively light, vibra tory jars tothe tamping stickv through theresilient gripping device. The hammer toolof the present invention is designed so that the tamping stick passesaxially through the tool and the resilient gripping device is fluidactuated and automatically grips the tamping stick at any desired pointalong its length whenever operating Huid is supplied to the tool.

An object' of the present invention is to provide an improved powerhammer for applying mechanical driving powertoa tamping stick fortamping powder or dyna mite into a hole that is to be charged.Anotherobject is to provide anl improved hammer tooll for imparting aseries of rapid, relatively light'vibratoryjars to a tamping stick. Yetanother object is to provide an improved tamping toolfor effectingtamping of a blasting charge. A further object is to provide` animproved hammer tool designed axially to surround and receive. a tampingstick and for gripping the latter whereby a mechanical driving force maybeimparted to the tamping stick at. the desiredpoint along its length. Astill further object is to provide an improved releasable resilientgripping device or yieldable clamp adapted to grip the exterior surfaceof a tamping stick for connecting a hammer tool to the stick whereby aseries of hammer blows may be imparted to the stick through the grippingdevice or clamp. Still another object is to provide an improved hammertool having novell features' of construction. These and other objectsand advantages of the invention will, however, hereinafter more fullyappear.

In the accompanying drawing there is shown for purposes of illustrationone form which the invention may assume in practice.

In this drawing:

Fig. l is a View partially in central longitudinal section and partiallyin side elevation of a power hammer constructed in accordance with anillustrative embodiment of the invention, and showing a tamping4 stickassociated therewith.

Fig, 2 is across sectiontaken on line 2;-2 of Fig. 1

2,693,733 Patented Nov. 9, 1954 2 through they power hammer and tampingstick, looking toward the rear end of' the power hammer.

Fig.` 3y is a cross section taken on line 3 3; of Fig. l.

Fig..4 is aragmentar-y section taken on'. theplaneof Fig. 1,.sho.wingthe control valvesin closed position.

52 is acrosssectional View taken; on line. 5;.-5 of ig;

Fig. 6. is a diagrammatic View showing a'. blast hole formed in theearth. orl rock strata with a blasting charge and tamping stickpositionedtherein and illustrating'the mannerof. operation of theimproved power hammer forkapplying'mechanical driving power to thetamping stic l'n thisl illustrative construction, as shown inthedrawing, the improved power hammer, generallyl designated l., is shownassociated with a tamping stick on rod 2. The tamping stick is ofcylindrical, rodlike formation and is desirably non-metallic andnon-conducting,` pref-V erably composed ofl hard wood, so that. there isno possibility of the creation of sparks generatedby static electricityoryby contact. with rock formation. The power hammer is. constructedwith an axiaLpassageway extending therethrough` for axially receivingthe tamping stick and may be' connected to the stick at any desiredpoint along the length of. the stick.

The power hammer is ud' operated and includes Aa so-called. valvelessmotor having a motor cylinder. 3 formed with an annular bore 4containing a reciprocable hammer piston S.V The motor cylinder has anintegral forward housing. 6A containing a releasable resilient grippingdevice or yieldable clamp or chuck 7 adapted to surround the tampingstick and to grip the exterior periphery of the tamping stick to connectthe power hammer thereto, as later more fully explained. A rear motorhead 8 is secured as by b'olts 9 to the rear end of the' motor cylinderand` has a tubular rearward extension 10 providing a handle 11 adaptedto be grasped by the operator whereby the hammer may be manuallypositioned and supported. The motor cylinder has a concentric innersleeve i2. providing the inner wall of the cylinder bore and the ends ofthis sleeve. are mounted in bores 13V and 14,. they former being formedin the rear cylinder head Sl and the latter being formed in a frontcylinder head l5 integral. with the front housing 6; The hammer pistonis of' cylindrical annular construction and slidingly engages theconcentric inner and outer walls of the motor cylinder, Vand has a frontannular impact surface 16,.

Now referring to the fluid distribution means for the motor cylinder itwill be noted that attached at 18 to one side. of the motor cylinder isa fluid inlet. pipe 19 which may supply iluid under pressure from anysuitable source to an inlet passage 20. Arranged parallel to thecylinder bore at one side of the cylinder is a longitudinal bore 21 inwhich a sleeve 22 is tted with the rear end of the sleeve abutting therear cylinder head, as shown in Fig. l. 'Ihe'iront end of the sleeve isformed with a conical seat 23 with which a conical endseating valve 24is engageable, and this valve has a stem 25 guided in the sleeve-boreand extending rearwardly through a bore 26 in the rear headk S. A coilspring 27 seatedl ina recess 23 engages the valve 24. for'urging thelatter toward its seat. Pivoted at 30 on pivot screws 31 secured to thesides of the tubular head portion 10 isanannulus 32 having an integrallever 33 provided with a grasping portion extending rearwardly along onesideof the handle 11 and adapted to fit closely to they side. of thehandle. This annulus at itsside opposite from the lever 33 car'- rics abolt 34 whose front head 35 is engageab'le. with the projectingl endof'thevalve stem 25'. The operator bypressing the. lever 33 toward thehandlev 11 may'swing the annulus 32 to effect movement of the valve stem25 to the right, as viewed in Fig. 1, to unseatl the valve 214 againstthe action of the coil spring 28. The frontend of the sleeve 22terminates a shortV distance from the front end of the bore 21 toprovide a chamber 35 inl which the valve 24. is'ar-ranged', and theinlet passage 20 communicates with this chamber. The sleeve 22 h as4 aperipheral.` groove 36 andA longitudinally spacedl ports 37 in the.sleeve connect the. sleeve bore with this groove; The valve stem is.peripherally groovedy or reduced. in cross section at 38 so that, whenthe. valve is unseated',

fluid may flow past the valve through the ports 37 to the groove 36.Longitudinally spaced ports 39 and 40 in the cylinder wall connect thegroove 36 with the cylinder bore 4 near the longitudinal center of thecylinder. The hammer piston is annularly grooved at 41 on its exteriorperiphery substantially midway between its ends. Longitudinally spacedexhaust ports 42 and 43 in the sleeve 12 are spaced equal distances fromthe ends of the cylinder bore, and the inner wall of the piston isannularly grooved or recessed at 44. There is an annular clearancespace, at 45, between the inner periphery of the sleeve 12 and theexterior surface of the tamping stick 2, and one or more exhaustpassages 46 in the rear head connect this clearance space to atmosphere.Formed in the opposite wall of the cylinder from the inlet valve 24 arelongitudinal supply passages 48 and 49, and longitudinally spaced ports50 and 51 connect the ends of the passage 4S with the cylinder borewhile longitudinally spaced ports 52 and 53 connect the opposite ends ofthe passage 49 with the cylinder bore. The ports 50 and 53 communicatewith the cylinderbore near its remote ends while the ports 51 and 52communicate with the cylinder bore at points nearer the longitudinalcenter thereof, and these latter ports 51 and 52 are communicable withthe exterior piston groove 41. A starting port 54 located at the innerside of the port 51, in adjacency thereto, connects the inner end of thepassage 4S with the cylinder bore so that when the hammer piston is inits centrally located position substantially midwayV between thecylinder-ends the port 54 may communicate with the exterior pistongroove 41.

The fluid distribution means for the motor cylinder functions in thefollowing manner: When the hammer piston is in its midstroke positionshown in Fig. l and the inlet valve 24 is opened, pressure uid may iiowfrom the inlet passage Ztl through ports 37 and lll and the exteriorgroove 41 on the piston to the port 54 and through passage 43 and port50 to the rear end of the cylinder bore at the rear side of the hammerpiston; the pressure fluid acting on the rear pressure iiuid of thepiston to drive the latter forwardly. As the piston moves forwardly theexternal piston groove 41 is moved into communication with the port 52thereby effecting iiuid flow through passage 49 to the front end of thecylinder bore, and as the piston moves forwardly its rear edge uncoversthe exhaust ports 42 connecting the rear end of the cylinder bore toexhaust. The pressure tluid in the front end of the cylinder bore actson the front pressure area of the piston to drive the latter rearwardlyto etect its return stroke. As the piston moves rearwardly f the port 52is covered by the piston and the exterior piston groove 41 is broughtinto communication with the ports 54 and 51, supplying pressure luid tothe passage 4S and port Si) to the rear end of the cylinder bore, and asthe piston approaches the rear end of its stroke the front end of thecylinder bore is connected to exhaust through exhaust ports 43, theannular clearance space 45, and the exhaust port 46. The pressure fluidin the rear end of the cylinder bore acts on the rear pressure area ofthe piston to drive the piston forwardly to effect its working stroke,and the operations above described are repeated in rapid sequence, toeffect rapid reciprocation of the hammer piston. The type of valvelessmotor disclosed is well known and does not per se enter into the presentinvention. Evidently, other types of hammer motors may be employedwithout departing from the spirit of the invention.

ln this improved construction, arranged at spaced points in the frontcylinder head 15 are longitudinal bores 56 in which striking blockplungers or tappets 57 are reciprocably mounted and these plungersproject rearwardly into the front end of the cylinder bore into aposition to receive the impact blows of the hammer piston. Arranged inthe bore 58 of the front housing 6 is a sleevelike member 59 and thismember is slidably mounted in the housing bore and contains an annularrubberlike mass or resilient annuius 60 which performs the function of agripping or clamping ring or bushing. rThis rubberlike annulus surroundsthe tamping stick Z which passes axially through the hammer tool. Theslidable sleevelike member 59 has a reduced front sleeve portion 61which is slidingly guided at 62 on the exterior surface of a guidesleeve portionl 63 integral with a front cap 64 Vthreadedly securedwithin the bore of the front housing 6. The member 59 carries a sealingring 65 sealingly engaging the housing bore and the sleevelike por tion63 carries a sealing ring 66 sealingly engaging the bore of thesleevelike portion 61. Guided in the bore 67 of the sleevelike body ofthe member 59 at the rear of the annulus 69 is an anvil ring 68 which isengaged by the plungers 57 as shown in Fig. l.. A passage 69 connectsthe spring recess 28 with an annular space 70 between the member 59 andthe front cap 64, for conducting pressure fluid to the space to act onthe front pres- -sure area of the member S9 to force the latterrearwardly in the housing bore 58 thereby to compress the rubberlikemass or annulus 60 into gripping engagement with the outer surface ofthe tamping stick 2. As the hammer piston of the hammer toolreciprocates in the cylinder bore a series or rapid, relatively lightblows are transmitted through the plungers 57, the anvil ring 68 and therubberlike mass or annulus 6i) to the tamping stick mechanically' todrive the latter inwardly to eifect the tamping operation. Thus, therubberlike mass not only serves to grip the tamping stick but alsotransmits the hammer blows to the stick so that a relatively lightvibratory jarring action on the tamping stick is eifected therebyrendering the mechanical tamping operation comparatively safe and withlittle eli'ort on the part of the operator.

Communicating with the passage 69 is a bore 71 at its inner endsurrounded by a valve seat 72 and a ball valve 73 in the bore isengageable with the seat to cut out ow of iluid from the valve chamber35 to the space 7). A plunger 74 reciprocably mounted in a plug 75threadedly secured to the cylinder wall, has a handle 76 whereby theplunger may be moved to engage and seat the ball valve. When the ballvalve is seated, as shown in Fig. 4, the space 70 may be vented toatmosphere through the passage 69, the bore 71 and grooves 77 in thebody of the plunger, thereby to effect release of the rubberlike mass orannulus 60 from gripping Yengagement with the tamping stick. When thegripping device is released the hammer tool may be moved axially alongthe tamping stick into diiferent positions, and may be bodily removedfrom the stick if desired.

As shown diagrammatically in Pig. 6 the blast hole in the earth or rockstrata is designated H and the blasting charge of powder or dynamite isdesignated C. The tamping stick or rod 2 may be inserted in the hole asshown and the power hammer tool may be slid onto the stick with thelatter passing axially through the tool in the manner shown. Fluid underpressure may then be supplied through supply pipe 19 to the tool and thepressure fluid flowing past the ball valve 73 through passage 69 to thespace 70 acts on the front pressure area of the member 59 to move thelatter rearwardly in the bore of the front housing to effect compressionof the rubberlike mass or resilient annulus to cause the latter to clampfirmly or grip the tamping stick. The operator supports the power tooland tamping stick by grasping the handle 11 and when the lever 33 isswung inwardly toward the handle the valve stem 25 is slid inwardly toVunseat 'the valve .24. Pressure luid may Vthen flow through thedistribution ports and passages to the motor cylinder to effect rapidreciprocation of the hammer piston thereby to deliver impact blowsthrough the plungers 57 and the anvil ring 63 to the rubberlike mass orresilient annulus 6l) and through the latter to the tamping stick. Thus,a series of rapid relatively light cushioned blows are mechanically1transmitted through the compressed resilient mass 60 to the tampingstick to vibrate or jar the latter in such manner as to eect eihcienttamping of the blasting charge in the bottom of the hole. The operatorgrasping the handle 11 of the hammer tool may move the tamping stickinwardly against the blasting charge as the tamping stick is vibrated.When tamping of the charge is completed the tamping stick'may bewithdrawn from the hole by pulling outwardly on the impact tool. As longas fluid under pressure is supplied to the supply pipe l@ and the bailvalve 73 is open the hammer tool cannot slip off from the tamping stick,but the gripping engagement of the tool with the tamping stick may bequickly released simply by pressing on the handle of the plunger 74toseat the ball valve 73 thereby to effect venting of the space '76 toatmosphere. Whenever 'the handle 33 is released by the operator theVinlet valve 24 is instantaneously seated by the coil spring 27 tointerrupt the fluid supply to the hammer motor.

As a result of this invention an improved hammer aanwas tool is providedfor mechanically imparting.' relatively lightjarslorvibrations to atampingk stick orirod whereby tamping; of a powder orf dynamite charge.in a hole formed in the earth or rock strata to'be blasted, iseected inan etlicient manner, and with comparative ease; and safety. By theprovision of the resilienty gripping device and by the passing of thetamping stickaxially through the impact tool, the tamping stick may bevgripped at any desired point along its length to-connect the-impact toolat the stick. The novel arrangementl for 'transmitting the blows of thehammer tool tothe tamping stick through the resilient gripping deviceenables the delivery of a series of rapid relatively light, cushionedblows to the tamping stick so that the latter may be mechanically drivenwith comparative'safety. The hammer tool is relatively simple andcompact and relatively light in weight yet is extremely efective inoperation. By the provision of the novel control valve the grippingdevice may be quickly released from the tamping stick and in the eventthe power tool is released bythe operator the'hammer motor automaticallystops. The rubberlike gripping annulus which is compressed by the actionof pressure uid into grippingv engagement with the tamping stickprovides for elective gripping: of the stick by the tool, substantiallyeliminating the possibility of slippage. These and other advantages ofthe invention will be clearly apparent to those skilled in the art.

While there is in this application specifically described one form whichthe invention may assume in practice, it will be understood that thisform of the same is shown for purposes of illustration and that theinvention may be modified and embodied in various other forms withoutdeparting from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

l. A power hammer tool for imparting vibratory jars to a tamping stickcomprising a hammer motor having an axial passage extendingV completelytherethrough for receiving a tamping stick and within which the latteris adapted to be variably axially positioned, a releasable grippingdevice carried by said tool for connecting said tool in the desiredposition to the stick and for maintaining the same in such connectedposition during the tamping operation, and means for transmitting thejars l set up within the tool through said gripping-device to thetamping stick.

2. A power hammer tool for imparting vibratory jars to a tamping stickcomprising a hammer motor having an axial. passage extending completelytherethrough for re.- ceiv-ing a tamping stick and within which thelatter is adapted for axial insertion, a releasable gripping devicecarried by said tool for connecting said tool to the stick at anydesired point along the length. of the latter and for maintaining thesame in such position-during the tamping operation, and means fortransmitting the jars set up within the hammer tool through saidgripping device to the stick to etect jarring of the latter.`

3. A power hammer tool Vfor imparting impacts to a tamping stickcomprising a hammering device having an axial passage therethrough forreceiving a tamping stick, a resilient` gripping'device. embodied in thetool for connecting the latter to the tamping` stick, means fortransmitting the hammer blows of saidhammering device to said grippingdevice whereby the hammer blows are imparted to the stick, uid actuatedmeans for actuating saidV gripping device to eiiect gripping of thetamping stick and for maintaining said gripping device in grippingposition during the tamping operation and operator controlled means forsubjecting said actuating means to the action of pressure fluid.

4. A power hammer for imparting vibratory jars toa tamping stick toeffect mechanical tamping of. a blasting charge, comprising a uidactuated hammer motor having an annular cylinder formed with an axialpassage for receiving a tamping stick, an annular hammer pistonreciprocable in said cylinder and surrounding.; said axial passage, agripping device carried within the front end of the hammer for grippingthe tamping stick and through which vibrations are transmitted to thestick, and reciprocatory plunger means cooperating with said grippingdevice for transmitting the piston blows to said gripping device toeffect vibration of the tamping stick.

5. A power hammer tool for imparting vibratory jars toa-.tamping stickto eiectmechanca-L tamping of a'V blasting charge,` comprising; alluidoperated hammer motorf including'a reciprocable hammer piston, ayieldable annular massy carried'by the tool, means: embodied in thetooll for effecting.; compression of saidv yieldable mass to causethelatter togrip the-tamping stick in the desired position completelyabout the-periphery of the stick and for maintaining said mass insuch.grippingl position during the tamping operation, and means fortransmitting the'blows ofi saidpistonto-said compressed yieldable massto eiectf vibrationaol thetamping stick.

In a hammer tool: of the character disclosed, a motor cylinder providedwith afront head'and-having'an axial passage extending, completelytherethrough for receiving a tamping stick, an annular: hammer pistonreciprocable in said cylinder. and surrounding; said axial passage, aplurality of spaced: plungers carried by and arranged in an annularseries about said: headfor receiving the impact blows of said piston;ananvil ring associated with said front head and to which: the hammerblows. are transmitted by said plungers, and af rubber.- like mass forgripping the tamping stick and. engaged by said ring and through whichthe piston blows are transmitted to the tampingjstick.

7. A hammer tool for imparting a series-of rapidrela tively lightblowsto a tamping stick ,comprisinga hammer device for receivingand-surroundinga tamping stick, and areleasable clamping device forconnecting the tool toV the tamping stick at any desired point along'thelength of theV latter. and for maintaining said. device inV suchposition during the tamping operation, and means for. transmitting thehammer blows of the tool through said. clamping device to the stick;

8. A mechanism for mechanically driving a tamping stick comprising apower hammer tool having an axial passage: extendingcompletelytherethrough for receiving a tamping stick, said toel havinganannular piston chamber surrounding saidaxialpassage and containinganannular hammer pistonthrough-which. said axial passage. extends,.areleasable-:chuck for connecting the tool to the tamping, stick at anydesired point along the length of the latter, and means forltransmittingV the pistonblows tosaid chuck to effect hammeringof thetamping stick.

9. A mechanismtor mechanically driving a tamping stick by imparting.Vibrationsv thereto including means forming a housing having a bore and.adapted tosurround a tamping stick', a resilient annular mass in saidhousing-bore;v means for transmitting the vibrations of saidfmechanismto'said annular mass andthence. to impartl such vibrationsA through saidmass. to' the stick, and meansv for effecting compression of saidresilient mass to cause. the latter togrip the tamping, stick completelyabout the periphery thereof and fory maintainingsaid resilient mass insuch gripping,V posi-tion; during the tampingl operation.

l0. A mechanism-for .mechanicallyl drivingta tamping stick by impartingvibrations thereto` including means formngahousing having aboreextending axially therethrough and adapted to. surround a. tamping stickand throughwlu'ch the latter extends, an annular plungerlike memberreciprocable in` said housing bore, a` resilient annular: masscontainedv in said reciprocable member and to which: vibrations i are.imparted by the4 mechanism, and: means for subjecting said reciprocablemember to the action of4 pressure Huid to etiect compression'aof: saidresilient massi to cause thei latter to: grip the tampingstickcompletelyab'out the periphery of' thestickl at' any desired` pointalong the lengthi of the' latter and to maintain. said mass in suchgrippingposition during the tamping opera-tion whereby the vibrationsare imparte-:l through' saidfmass' to the stick.

ll. A mechanism forv mechanically driving a tamping stick by impartingvibrations thereto' including means forminga housing having a boreextending axially therethrough and adapted to surround' a tamping stickand through which the-latter extends, aplungerlike. member reciprocableVin said housingY bore; a resilient annular mass contained in=lsaidreciprocable member, a ring arranged in said housing-bore at one endof said member and engaging said resilient mass for transmittingvibrations to the latter, and means for subjecting the opposite end ofsaid reciprocable member to the action of pressure fluid for effectingcompression of said resilient mass against said ring to cause said massto expand inwardly to grip the tamping stick at any desired point alongthe length of the latter and for maintaining said mass in such grippingposition during the tamping operation whereby the vibrations areimparted through said mass to the stick.

12. A mechanism for mechanically driving a tamping stick by impartingvibratory blows to the latter including means forming a housing having abore 'and extending axially therethrough and adapted to surround atamping stick and through which the latter extends, a reciprocableplungerlike member contained in said housing bore, a resilient annularmass contained in said reciprocable member, an anvil ring arranged 4insaid housing bore at one end of said member and engaging said resilientmass for transmitting vibratory blows to the latter, means forsubjecting the opposite end of said reciprocable member to the action ofpressure fluid for effecting compression of said resilient mass to causethe latter to expand inwardly to grip the tamping stick at any desiredpoint along the lengthpf the latter and for maintaining said mass ingripping position during the tamping operation, and means fortransmitting vibratory blows to said ring torsaid cornpressed resilientmass whereby such blows are imparted to the tamping stick.

13. A hammer tool for imparting a series of rapid, relatively lightblows to a tamping stick comprising a hammer motor having an annularcylinder providing an axial passage through which the stick is adaptedto extend, a front head for said cylinder, an annular hammer pistonreciprocable in said cylinder and surrounding said axial passage, aseries of reciprocatory plungers mounted in spaced circular relationabout said front head and projecting into said cylinder in a position toreceive the piston blows, an anvil ring associated with said front headto which the piston blows are transmitted by said plungers and means foroperatively connecting the tool to the stick so that the blows impartedto said ring are transmitted to the tamping stick.

14. A hammer tool for imparting a series of rapid, relatively lightblows to a tamping stick comprising a hammer motor having an annularcylinder providing an axial passage through which the stick is adaptedto extend, a front head for said cylinder, an annular hammer pistonreciprocable in said cylinder and surrounding said passage, a series ofreciprocatory plungers mounted in spaced circular relation about saidfront head and projecting into said cylinder in a position to receivethe piston blows, an anvil ring associated with Vsaid front head towhich the piston blows are transmitted by said plungers, and a chuckassociated with said ring and engageable with the tamping stick andthrough which the blows from said ring are imparted to the tampingstick.

15. A hammer tool for imparting 'vibratory jars to a tamping stick andembodying means for setting up vibratory jars, a releasable grippingdevice attachable to the tamping stick at any desired point along thelength of the stick and for maintaining the same in such position duringthe tamping operation, means for effecting attaching engagement of saidgripping device with the stick, and means for transmitting suchvibratory jars through said gripping device to the stick.

16. A hammer tool for imparting a series of rapid, relatively lightblows to a tamping stick comprising a hammer motor including a motorcylinder having an annular piston chamber and provided with an axialopening extending completely therethrough for receiving a tamping stick,said chamber having its inner wall surrounding said axial opening andthere being a clearance space between the wall of said axial opening andthe exterior periphery of the stick, an annular hammer pistonreciprocable in said piston chamber and surrounding said axial opening,and uid supply and exhaust means for said motor including passages forsupplying iluid under pressure to said piston chamber and exhaust portsin the inner wall of said piston chamber and opening into said axialstick-receiving opening, said exhaust ports controlled by said pistonand communicating with said clearance space.

17. A hammer tool for imparting a series of rapid, relatively lightblows to a tamping stick comprising a hammer motor including a motorcylinder having an annular piston chamber and provided with an axialopening extending completely therethrough for receiving a tamping stick,said chamber having its inner wall surrounding said axial opening andthere being a clearance space between the wall of said axial opening andthe exterior periphery of the stick, an annular hammer pistonreciprocable in said piston chamber and surrounding said axial opening,fluid supply and exhaust means for said motor including passages forsupplying iluid under pressure to said piston chamber and exhaust portsin the inner wall of said piston chamber and opening into said axialstick-receiving opening, said exhaust ports controlled by said pistonand communicating with said clearance space, and an exhaust passage in awall of said motor cylinder for connecting said clearance space with theexterior of said hammer motor.

18. A hammer tool for imparting a series of rapid, vibratory jars in aforward direction to a tamping stick comprising a hammer motor having ahousing and provided with an axial opening completely therethrough forreceiving a tamping stick, a iluid actuated chuck for yieldinglyconnecting said hammer motor to the tamping stick at any desired pointalong the length of the latter and including a yieldable grippingelement, and uid actuated means acting in a rearward direction foreffecting gripping of the stick by said yieldable element and formaintaining the latter in gripping position during the tampingoperation, and said hammer motor including a hammering element forimparting longitudinal impulses in a forward direction to said yieldableelement whereby such impulses are imparted through said yieldableelement to the stick, said uid actuated means acting in opposition tothe forward impulses imparted by said hammering element.

19. In combination, a tamping stick, a yieldable element clamped in apredetermined position to said stick for transmitting longitudinalimpulses thereto during the tamping operation, hammering means includinga casing having blow-striking means reciprocable relative thereto fortransmitting longitudinal impulses to said element in one direction toeffect vibration of the stick, and means forming a yielding cushionbetween said element and said casing acting upon said element oppositelyto the direction of such impulses.

20. In combination, a tamping stick, a yieldable element maintainedclamped in the desired position to said stick for transmitting forwardlongitudinal impulses to said stick during the tamping operation,hammering means including a casing having blow-striking meansreciprocable relative theretoV for transmitting longitudinal impulses tosaid element in one direction to effect vibration of the stick, andmeans forming a yielding cushion between said element and said casingacting upon said element oppositely to the direction of such impulses,said cushion forming means including a member urged in such oppositedirection byuid under pressure and operator controlled means forsubjecting said member to the action of pressure fluid.

References Cited in the le of this patent Y UNITED STATES PATENTS NumberName Date 608,953 Carlinet Aug. 9, 1898 1,082,137 Pierce Dec. 23, 19131,346,064 Remmen July 6, 1920 1,372,009 Davidson et al Mar. 22, 19211,499,569 Bailly July 1, 1924 1,621,663 Gartin Mar. 22, 1927 1,788,034Smith Jan. 6, 1931 1,844,874 Smith Feb. 9, 1932 2,413,542 Butts Dec. 31,1946 2,469,198 La Pointe May 3, 1949 2,561,577 Knudsen July 24, 19512,563,464 Green Aug. 7, 1951

